1. Field of the Invention
The present invention relates to a method of manufacturing ceramic sintered bodies by means of a hot press method.
2. Description of Related Art
A pressurized sintering method of ceramics by means of a hot press method is generally used for sintering various kinds of ceramics such as silicon nitride, silicon carbide and aluminum nitride. Such a sintering method is applied for manufacture of electric materials such as ferrite for a magnetic head, ferroelectric piezoelectric ceramics, transparent ceramics and transparent piezoelectric ceramics.
The applicant disclosed, in Japanese Patent Laid-Open Publication No. 5-251365 (JP-A-5-251365), a hot pressing of aluminum nitride ceramics to manufacture a substrate for a semiconductor manufacturing apparatus such as a ceramics heater, a ceramics electrostatic chuck, a ceramics high frequency electrode apparatus and a ceramics susceptor. In the method mentioned above, when a formed body made of aluminum nitride powders is accommodated in a hot press apparatus, a graphite foil is arranged between the formed body and a sleeve and between the formed body and a spacer, in order to control the environmental atmosphere of the formed body and also to prevent a reaction between the formed body and the sleeve or the spacer.
In the semiconductor manufacturing apparatus, it is known that a sintered body having a dome shape is used as an electrode for plasma generation by embedding a metal member in the sintered body having a dome shape and conducting electricity through the metal member.
However, in the known hot press method, it is thought to be difficult to obtain a sintered body having an irregular shape other than a planar shape because the shrinkage of the formed body along the pressure applying axial direction is extremely large. On the other hand, the thickness of a ceramic sintered body having an irregular shape is largely varied corresponding to a position on a surface of the ceramic sintered body along a pressure applying axial direction. Therefore, it is thought that pressure is not uniformly applied to various portions of the formed body and the portions are then not uniformly heated.
Therefore, in order to manufacture a sintered body having, for example, a dome shape, a sintered body having a large plane shape is first manufactured by means of the hot press method, and then the thus manufactured sintered body is ground. However, such a grinding step involves a large amount of time. In addition, when a metal member, such as an electrode, is embedded in the sintered body having a plane shape, it is extremely difficult to correctly measure the portion in the sintered body at which the metal member is embedded and grind the sintered body corresponding to the portion of the metal member. Therefore, the drawback is that the embedded position of the metal member is liable to be shifted from a designed normal position.